(1) Field of the Invention
This invention relates to polymer composites. More particularly, this invention relates to a technique for grafting organic materials as such, or mixed with an inorganic material, with a silylating agent. Bonding the silylated material with a polyolefin resin produces either composites having improved physicomechanical properties, or composites having only strongly bonded components.
(2) Description of Prior Art
The modification of the physical and mechanical properties of thermoplastic, thermosetting or rubbers by the addition of a filler is well known in the art. Greater degrees of property improvement result when the filler is uniformly and highly dispersed throughout the polymer matrix and/or when its chemical interface provides a possible site weakness in the composite.
Various means for improving the compatibility of the filler with the polymer matrix by providing an interaction between the filler and the polymer are known in the art. For example, when a cellulosic material, such as wood fibers, or cotton fibers, are used as a filler in the polymers containing methylol groups such as phenolic urea or melamine resins, a reaction occurs between the methylol groups and the hydroxyl groups on the cellulosic filler. Inorganic fillers such as calcium carbonate, clay or asbestos have been encapsulated and dispersed in a polyolefin in order to obtain improved properties. Some materials such as maleic anhydride or others were bonded by the effect of the initiating agents such as peroxides. In such a system, the polymer used to coat the filler should be chemically bonded to the filler in order to obtain optimum properties such as high strength.
The E.P. Pat. No. 0008143-Solvay & Cie, issued in Feb. 20, 1980, and the Japanese Pat. No. J5 8011-537- Showa Den Kokk, issued on Jan. 22, 1983, both teach the application of organic and/or inorganic fillers in presence of a peroxide and an acid anhydride, resulting in composite materials having relatively little improvements in their mechanical strengths.
The Japanese Pat. No. J5 719 2-466 Showa issused in May 5, 1981, teaches the addition of an unsaturated silane coupling agent onto the polyolefin matrix material by the effect of a catalyst peroxide and then by adding a wood flour to act as a filler. The composite materials produced according to this reference have improved impact strength, but, in comparing their relative improvement values with those realised by the present invention they were found much lower, because the silane coupling agent was grafted onto the polymer resin and was not grafted onto the cellulosic filler material. Grafting and bonding of a silylating agent onto cellulosic fibers whether premixed or not with an inorganic filler leads to producing composite materials having dramatic higher physicomechanical properties beside their high durability and resistivity to heat, cold and solvents. It should be noted that the silane ratios added according to the present invention can be lowered by prehydrolysing in acid medium which leads to cost economy.
According to the present invention, the silane grafting and bonding process creates strong attachments between the mixture of components and the silylating agent. The grafting process could either be partial or complete. The process could be completed by the effect of a hot molten polymer resin, which provides sites for the formation of free radicals with desired degrees of loading by the initiation effect to attach by chemical bonding to the other side of the silylating agent molecules, which are pregrafted and prebonded with the mixture of materials. Thus, for example, the flow properties of polyethylene are improved by the incorporation of the grafted filler mixture in the presence of maleic anhydride and a free radical catalyst such as benzoyl peroxide. The composition ratios range from 1 to 99% by weight of the grafted and bonded silylated materials.